1. Field of the Invention
The present invention relates to a production process of an amino acid-N,N-diacetic acid (hereinafter may be referred to as xe2x80x9cAADAxe2x80x9d) or its salt with an equivalent or less of an alkali metal, with efficiency, by reducing alkali metal ions from an aqueous solution of an alkali metal salt of an AADA. To be more specific, it relates to a process of an aqueous solution of an AADA salt low in pH or an acid form of AADA in high yield by reducing alkali metal ions from an aqueous solution of an AADA alkali metal salt, and to a process for producing a salt of an AADA.
2. Description of the Prior Art
Metal salts and amine salts of ethylenediaminetetraacetic acid (hereinafter may be referred to as xe2x80x9cEDTAxe2x80x9d) or diethylenetriaminepentaacetic acid (hereinafter may be referred to as xe2x80x9cDTPAxe2x80x9d) have been used as, for example, detergent additives, trace metal element fertilizers for agricultural use, and photographic agents. In particular, iron salts and ammonium salts of EDTA and DTPA have been used in large quantities as oxidizing agents for color photography printing. These chelate salt compounds are, however, hardly biodegradable, and therefore a variety of highly biodegradable chelate salt compounds derived from material amino acids have been developed as alternatives to these compounds, from the viewpoint of environmental protection in recent years. Among them, AADA salts receive attention for their high biodegradability. Of these AADA salts, glutamic acid-N,N-diacetic acid (hereinafter may be referred to xe2x80x9cGLDAxe2x80x9d) derived from glutamic acid is most demanded.
As production process for AADA salts, processes of reacting a corresponding amino acid with sodium monochloroacetate (Japanese Unexamined Patent Publication No. 6-59422) as a laboratory-scale production process, or with sodium cyanide and formalin (U.S. Pat. No. 2,500,019) as a commercial-scale production process are generally employed. In any process, a solution of an AADA sodium salt is produced which contains sodium ions in large amounts and shows a strong alkalinity. Therefore, the solution shows poor compatibility and cloudiness or precipitates may form when it is mixed with a detergent. Furthermore, such a solution cannot be used as intact as a material for shampoos and other products that will be used with pH value around neutrality.
In addition, for the production of metal salts, ammonium salts and amine salts of an AADA, such an AADA containing sodium ions is generally used as a material and reacted with an inorganic or organic acid. According to this process, however, an alkali metal salt of the inorganic or organic acid is by-produced and thus a high purity chelate metal salt cannot be obtained. In the production of GLDA iron salts, which are important as photographic agents among these metal salts of AADA, an ammonium salt of GLDA is generally reacted as a material with iron nitrate. According to this process, however, by-produced ammonium nitrate in coexistence becomes a problem.
On this account, demands have been made to provide an AADA, which contains no sodium ion, to be used as a material.
In this connection, the acids of EDTA and DTPA, which have been conventionally used, are low in solubility, and crystals of these acids containing no sodium ion can be obtained with facility by adding sulfuric acid or hydrochloric acid to decrease pH. AADA is, however, high in solubility, and crystals of its acid containing no sodium ion can hardly be obtained even by decreasing pH, or if obtained, it is obtained in low yield which invites increased costs.
The following processes have therefore been attempted: a process of adding an inorganic acid to a solution of an AADA sodium salt to acidify the solution, and precipitating and recovering an AADA salt by the use of an organic solvent as a bad solvent; a process of removing alkali metal ions with the use of an ion exchange resin; and a process of adding sulfuric acid to form sodium sulfate and thereby to remove alkali metal ions.
According to the process of precipitating and recovering the AADA salt by the use of an organic solvent as a bad solvent, the solubility of an inorganic salt in coexistence also decreases, which invites the contamination of the inorganic salt in the product AADA. To minimize the contamination of the inorganic salt, the amount of the organic solvent to be added must be decreased, but the yield of the product AADA decreases with a decreasing organic solvent.
The process of using an ion exchange resin is a process to be used as a means for removing a low concentration alkali metal ion but is improper as a means for removing such high concentration sodium ions as in the AADA reaction mixture. This is because a large quantity of an ion exchange resin is required to remove high concentration sodium ions and the resultant resin should be regenerated at frequent intervals, resulting in a deteriorated productivity. In addition, the AADA salt attached to the ion exchange resin is released into a wastewater during the regeneration of the resin, resulting in a very low yield of the AADA salt.
According to the process of adding sulfuric acid to form sodium sulfate and thereby to remove sodium ions, the concentration of sodium ions in an aqueous solution of the AADA salt cannot be reduced to such a low concentration of 3% or less, because sodium sulfate is high in solubility even at low temperatures. In addition, this process is highly disadvantageous in that sulfate ions are contaminated into the aqueous solution of the AADA salt.
The present invention has been accomplished to solve the above problems. Accordingly, it is an object of the invention to provide a process for an alkali metal salt of an AADA salt.
It is another object of the invention to provide a process for metal salts, ammonium salts or organic amine salts of an AADA with efficiency.
A further object of the invention is to provide a process for a solution of a magnesium salt of an AADA with efficiency.
Yet another object of the invention is to provide a bleaching agent composition containing a magnesium salt of an AADA such as mentioned above.
It is another object of the invention to provide a process for a solution of an iron salt of an AADA with efficiency.
A yet further object of the invention is to provide a process for crystals of an ammonium ferric salt of glutamic acid-N,N-diacetic acid with efficiency.
The invention provides a process for the production of an AADA, represented by the following formula (1), or its salt with an equivalent number or less of alkaline metals, the process includes: reducing alkali metal ions from an aqueous solution of an alkali metal salt of an AADA by electrodialysis. 
(wherein M represents an alkali metal, m represents 0 or an integer of from 1 to 2, and n represents 0 or an integer of from 1 to 3)
The invention provide, in another aspect, a process for the production of a salt of an AADA salt, the process includes: reacting an AADA with a compound selected from an metal oxide, a metal hydroxide, a metal carbonate, a metal hydrogencarbonate, an ammonium hydroxide, an ammonium carbonate, an ammonium hydrogencarbonate, or an organic amine compound.
The invention provides, in a further aspect, a process for the production of a magnesium salt of an AADA, the process includes reacting an AADA, which is obtained by electrodialysis, with a compound selected from a magnesium oxide, a magnesium hydroxide, a magnesium carbonate or a magnesium hydrogencarbonate. The invention provides, in yet another aspect, a process for the production of a salt of magnesium compound having an improved hygroscopicity by reacting 0.5 to 1 equivalent of a magnesium compound with 1 equivalent of a carboxyl group.
In another aspect, the invention provides a bleaching agent composition composed of a magnesium salt of amino acid and an oxygen bleaching base.
The invention provides, in a further aspect, a process for the production of a solution of a solution of an iron salt of an AADA, which process includes the steps of electrodialyzing an aqueous solution of an alkali metal salt of an AADA with the use of a hydrogen ion permselective membrane on the anode side and a cation permeable membrane on the cathode side to give an AADA, and reacting the obtained AADA with an iron oxide or metallic iron.
In addition, the invention provides a process for the production of a crystal of an ammonium ferric salt of glutamic acid-N,N-diacetic acid, which process includes adjusting the pH of a solution of an ammonium ferric salt of glutamic acid-N,N-diacetic acid to the range from 2.5 to 5.0 to crystallize and separate an ammonium ferric salt of glutamic acid-N,N-diacetic acid.
The invention further provides a crystal of an ammonium ferric salt of glutamic acid-N,N-diacetic acid.